1. Field of the Invention
The present invention relates to a spool valve having notches provided in a step between a land and a groove in a spool.
2. Description of the Related Art
Such a spool valve is known from Japanese Utility Model Registration Nos. 2568961 and 2580463.
FIGS. 9 and 10 show the structure of a conventional pressure-controlling spool valve having a proximal end toward a direct drive-type linear solenoid 26 and a distal end away from the solenoid. An input port 13, an output port 14, a drain port 15 and a feedback port 16 are open along an axis, L, into a valve bore 12 which is circular in cross section and defined in a valve housing 11. A spool 17 is slidably received in the valve bore 12 in the valve housing 11 and includes a first land 18, a second land 19, a third land 20, a spring seat 21 extending from a distal end of the third land 20, a first groove 22 defined between the first land 18 and the second land 19, a second groove 23 defined between the first land 18 and the third land 20, and a solenoid connection 24 extending from a proximal end of the second land 19. The spool 17 is biased proximally by a valve spring 25 disposed between an end of the valve bore 12 and the spring seat 21 to coaxially abut against a distal end of an output rod 27 of the direct drive-type linear solenoid 26 for directly operating the spool 17.
The first groove 22 in the spool 17 is connected to a proximal end of the first land 18 through a first step 28. The first step 28 is perpendicular to the L-axis and axially disposed from the second land 19 through a second step 29 perpendicular to the L-axis. A predetermined number of (e.g., four) notches 30 are defined in the first step 28 by chamfers inclined at 30xc2x0 with respect to the L-axis. When the spool 17 is in a position as shown in FIG. 9, the input port 13 is in communication with the output port 14 through the first groove 22. When the spool 17 is moved proximally, to cut off the communication between the input port 13 and the first groove 22, the output port 14 is brought into communication with the drain port 15 through the first groove 22. A feedback pressure is applied to an oil chamber 31 provided distally of the third land 20 through the feedback port 16. An oil chamber 32 defined between the first land 18 and the third land 20 communicates with the spool 17 through an oil bore 33 defined to connect the first groove 22 and the second groove 23 to each other.
In the spool valve having the above-described arrangement, when the linear solenoid 26 is excited to drive the output rod 27 distally, thereby urging the proximal end of the spool 17 against a repulsive force of the valve spring 25, the input port 13 is put into communication with the output port 14 through the first groove 22, such that the hydraulic pressure in the input port 13 is reduced depending on the opening degree thereof and delivered from the output port 14. In this case, the amount of pressure changed in the output port 14 relative to the amount of change in position of the spool 17 can be decreased to inhibit a self-induced vibration of the spool 17.
In the above prior art, the oil supplied from the input port 13 is passed through the notches 30 into the first groove 22. The oil flows within the first groove 22 in the direction of the L-axis to collide with the second step 29, thereby producing a flow force Fo for biasing the spool 17 proximally. The flow force Fo acts to oppose a distal drive force Fs generated by the linear solenoid 26, causing the smooth operation of the linear solenoid 26 is obstructed. As a result, it is difficult to conduct a subtle hydraulic pressure control.
Accordingly, an object of the present invention is to ensure that the notches are defined in the spool to suppress the generation of a flow force, thereby stabilizing the operation of the spool valve, while preventing the generation of vibration.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided a spool valve comprising a valve housing having a valve bore, an input port and an output port axially spaced within the valve housing and opening into the valve bore. A spool is received in the valve bore for sliding movement in the axial direction. A first land and a second land are formed on the spool and spaced along the axis. A groove is defined in the spool and connected to the first and second lands through first and second steps. A notch is formed by a cutout portion from the first step. Also, an actuator drives the spool in the axial direction, so that the spool is driven by the actuator to put the input port into communication with the groove. When the input port is put into communication with the groove, a fluid flowing into the groove through the input port is discharged from the output port through the groove. The notch in the spool is formed so that a line, which extends through a communication zone provided upon communication of the notch with the input port, and which forms a free flow-in angle with respect to the axial direction, first intersects a bottom of the groove.
With the above arrangement, when the notch is put into communication with the input port, the fluid flowing into the groove through the communication zone does not collide with other portions of the spool, before colliding with the bottom of the groove. Therefore, the flow of the fluid in the axial direction, which causes the flow force applied to the spool, is suppressed and the load on the actuator is decreased. Thus, it is possible to decrease the flow force applied to the spool to achieve the stable operation of the spool valve, while preventing the self-induced vibration of the spool as a result of the notch cut out from the first step.
According to a second aspect and feature of the present invention, the free flow-in angle is 69xc2x0, which corresponds to a maximum free flow-in angle. Hence, even if the free flow-in angle becomes equal to 69xc2x0, corresponding to the maximum free flow-in angle in accordance with the shape of the notch and the opening degree of the input port, the flow force applied to the spool can be suppressed so as to be small.
According to a third aspect and feature of the present invention, the notch is formed in a direction perpendicular to the axis. The notch can be made by an end mill, resulting in enhanced workability.
According to a fourth aspect and feature of the present invention, there is provided a spool valve comprising a valve housing having a valve bore, an input port and an output port defined in the valve housing and spaced along an axis and opening into the valve bore. A spool is received in the valve bore for sliding movement in the axial direction. A first land and a second land are formed on the spool and spaced along the axis. A groove is defined in the spool and connected to the first and second lands through first and second steps, respectively. A notch is formed as a cutout portion from the first step, and an actuator for driving the spool in the axial direction, puts the input port into communication with the groove, so that a fluid flowing into the groove through the input port is discharged from the output port through the groove. A concave curved face is formed on a bottom of the groove. The notch in the spool is formed so that a line, which extends through a communication zone provided upon communication of the notch with the input port and which forms a free flow-in angle of a jet formed by the notch, points to a portion of the curved face displaced from a smallest-diameter portion toward the first step.
With the above arrangement, a fluid flowing into the groove upon communication of the notch in the spool with the input port, before colliding with the bottom of the groove, does not collide with other portions of the spool. Therefore, the momentum of the fluid causing a flow force applied to the spool can be suppressed to decrease the load on the actuator. Particularly, a portion, against which the fluid flowing into the groove through the communication zone first collides, is that portion of the concave curved face formed in the groove, which is displaced from the smallest-diameter portion toward the first step. Therefore, the fluid is guided to the curved face, where the fluid is then turned smoothly and radially outwards. Hence, the flow force can be effectively be further decreased. Thus, the flow force applied to the spool can be decreased to ensure the stable operation of the spool valve, while preventing the self-induced vibration of the spool because of the notch in the first step.
According to a fifth aspect and feature of the present invention, the portion of the curved face displaced from the smallest-diameter portion toward the second step points toward the output port. Hence, the fluid can be guided smoothly to the output port, so that the flow force can be further decreased.
According to a sixth aspect and feature of the present invention, the free flow-in angle is 69xc2x0, which corresponds to a maximum free flow-in angle. Hence, even if the free flow-in angle becomes equal to 69xc2x0 corresponding to the maximum free flow-in angle in accordance with the shape of the notch and the opening degree of the input port, the flow force applied to the spool can be suppressed so as to be small.
According to a seventh aspect and feature of the present invention, the notch is formed in a direction perpendicular to the axis. Hence, the notch can be made by an end mill, resulting in enhanced workability.
According to an eighth aspect and feature of the present invention, the notch comprises a face extending contiguously from the communication zone to the curved face. Hence, the fluid flowing into the groove through the communication zone can be guided to the output port with the momentum thereof suppressed to the minimum, so that the flow force applied to the spool can be further decreased.
A linear solenoid 26 in each of embodiments corresponds to the actuator of the present invention, and a first groove 22 in each of the embodiments corresponds to the groove of the present invention.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.